The preferred embodiment concerns a method in which a speed difference is generated in a transfer printing region between an image carrier and a carrier material. The preferred embodiment also concerns a device for implementation of the method.
High-capacity printing systems for printing of a paper web are known from the documents DE 103 38 496 B3 and DE 103 38 497 A1, in which toner images present on the transfer belt are transfer-printed onto the paper web at a transfer printing point. The drive speed of the transfer belt is preset somewhat greater than the transport speed of the paper web, whereby a speed difference is present between the paper web 12 and the transfer belt. The speed difference is advantageously in the range from 0.1% to 10%, in particular in the range from 0.5% to 3% given a printing speed from 0.9 to 2 m/sec.
A printing system for printing of an endless paper web is known from the document U.S. Pat. No. 6,068,172, which printing system has a device for length compensation of a paper web to be printed in order to generate a preset tensile stress of the paper web in a transfer printing region.
A method and a device for transport of a web-shaped recording medium are known from the document DE 198 28 388 C2, in which method and device a length compensation element is provided with which a sensor is functionally coupled in order to determine the speed difference between a transport device arranged before the length compensation element and a transport device arranged after the length compensation element.
From the document U.S. Pat. No. 6,246,856 B1 a high-capacity printer and high-capacity copier is known in which toner images are generated that are transferred onto a recording medium. A plurality of developer stations are arranged along a photoconductor belt for generation of multi-color toner images, via which developer stations the color separations of a multi-color toner image are generated. The generated toner images of the color separations are successively transferred onto a transfer belt, whereby the individual color separations are thereby printed atop one another in registration. The color separations are thereby collected on the transfer belt. In a feed module what is known as a loop snag is provided via which the tensile stress of the carrier material to be printed is kept relatively constant.
A correct speed difference between the transfer belts serving as image carriers or the transfer belt serving as an image carrier and the carrier material to be printed is a decisive variable for the quality of the transfer printing of toner images onto the carrier material. If the speed difference is too great or too small, disruptions in the print image (for example what are known as wipes) arise or, for example, folds are formed in the carrier material to be printed. The carrier material can flutter in the region before the transfer printing point due to such folds, whereby the transfer printing conditions in the transfer printing region vary continuously. The actual speed difference does not remain constant due to various tolerances of arrangements for direction and propulsion of the carrier material as well as for direction and propulsion of the image carrier as well as variations of the direction and of the propulsion of the image carrier and of the carrier material during the print operation. The speed difference cannot be set or maintained exactly both over a longer image generation process and due to aging and/or wear of components of a printer or copier.